Research in high energy physics, primarily concerning the Mu2e experiment at Fermilab
The experiment's motivation arises from the surprising fact that the Big Bang was not immediately followed by an implosion driven by the gravitational effects of the enormous (and entirely unavoidable) vacuum energy associated with quantum fluctuations in the fields of the elementary particles that are contained in the Standard Model.
It is possible that the underlying equations of physical reality carry a mathematical space-time symmetry dubbed "Supersymmetry," or "SUSY" for short. If so, then the familiar particle zoo of quarks, leptons, and gauge bosons (the force-carrying messengers of the fundamental interactions) have as-yet unobserved cousins with spins that differ by half a unit of angular momentum. The spin-1/2 photino is related to the familiar spin-1 photon, and so on. The contribution of the SUSY partners (if they should exist) to the vacuum energy of quantum fluctuations enters with opposite sign to those of the associated "normal" particles. This difference in sign might allow SUSY effects to cancel the vacuum energy density that should have "recollapsed" the universe an instant after the Big Bang. The LHC at CERN will search for SUSY particles produced in high energy proton-proton collisions; Mu2e will seek them indirectly through their possible roles as mediators of otherwise-forbidden transitions such as neutrinoless muon-electron conversions that might take place in the (energy- and momentum-balancing) field of a nucleus.
The experimental signature of a conversion event will be the production of an electron that carries off nearly all of the muon's total energy, escaping from the aluminum nucleus that had bound its parent muon and traveling through the Mu2e spectrometer, which will measure its energy and momentum. A signal electron's energy will be very close to the muon's rest energy
The predominant source of background electrons is likely to come from the most common decay mode of muons into an electron, a neutrino, and an anti-neutrino. Since the muon's energy is shared among the electron, neutrinos, and aluminum nucleus, daughter electrons from this decay mode will tend to have considerably less energy than expected for signal electrons. However, a small fraction of these decays will yield electrons with energies only slightly less than that for signal electrons. It is possible that this will be the most troublesome source of background for the experiment, and it will be important that the collaboration understand how noise, instrument failures, and other problems might cause mundane events to misreconstruct as signal events.
It is also possible that very rare situations, in which multiple problems arise simultaneously, could also contribute to backgrounds.
The UIUC Mu2e group works primarily on technical issues relating to the design of a linac-based calibration system as well as the suppression of noise and backgrounds from protons, muons, and pions in the detector. We are also beginning to turn our attention to the design of the Mu2e calorimeter electronics as well as the possible use of NCSA's supercomputing resources in background modeling. Because many of the problems require a working knowledge of classical mechanics and electrodynamics, most of our research projects lend themselves well to the participation of undergraduate research assistants. The undergraduates in the group are scientists, not technicians, and find solutions to problems that have stumped PhD-level physicists. Results produced by the students have featured prominently in presentations at international conferences. At the moment, seven members of the HEP Mu2e group at UIUC are undergraduate physics majors. It is a great deal of fun for all of us.
We are exploring a number of issues relating to the design and operation of the Mu2e detector. See the documents, listed below, for detailed information. In particular, we have been investigating:
Design and performance of a linac-based calibration system in which electrons are injected into the downstream end of the Mu2e detector;
An improved geometry for the polyethylene proton absorber that immediately follows the Mu2e stopping target;
Use of dE/dx and timing information to suppress backgrounds from muons and pions.
We expect to undertake the following studies in the near future:
Performance of the energy-measuring electromagnetic calorimeter as a function of ADC system design;
Use of supercomputing resources available through NCSA in high-statistics simulations of Mu2e.
Reports and presentations
Five students are hard at work during the 2011 spring/summer terms. Here's what we're doing:
Transitioning from MatLab simulations of Mu2e to Geant4-based codes
Mapping (downstream) calibration electron injection phase space onto signal electron phase space to determine the feasibility of using downstream injection as a Mu2e calibration technique
Optimizing the geometry for a helical proton absorber and external shell
Investigating positron-electron differences inside the Mu2e spectrometer
Studying the performance of a helical geometry electromagnetic calorimeter
Two students wrote reports on their work in 2010.
Behavior of Calibration Electrons in the Mu2e Tracking Chamber, Devyn Shafer, George Gollin, Jason Dove
Mu2e Linac Analysis, Jason Dove, George Gollin, Devyn Shafer.
We made a roadtrip to Fermilab for the Mu2e collaboration meeting August 7, 2009.
Our August 2009 PowerPoint presentations:
Linac-Based Calibration System for the Mu2e Experiment, George Gollin, John Alsterda, Grace Bluhm, Sam Furnival, Tim He, Guangyong Koh
dE/dx and Particle Identification Inside L-Tracker, Matt McHugh
Rethinking the Proton Absorber Geometry, Daniel Pershey
Technical memos we wrote for the August 2009 meeting:
Mu2e Calibration: Electron Spectrometer and Magnetic Fields, John Alsterda et al.
Mu2e Experiment at Fermilab: Calibration with Linac and Collimation System, Grace Bluhm et al.
Electron Transport Line for Mu2e Calibration System, Tim He et al.
Feasibility Studies on a Downstream Injection System for Mu2e Calorimeter Calibration Electrons, Guangyong Koh et al.
dE/dx and Time-of-Flight Considerations For Particle Identification in the Mu2e Detector, Matt McHugh et al.
Analysis of a Novel Proton Absorber Geometry for the Mu2e Experiment, Daniel Pershey et al.
Other documents, some regarding Mu2e and some on other HEP subjects:
Thoughts concerning on-orbit injection of calibration electrons through thin-target elastic scattering inside the Mu2e solenoid, January 12, 2009 (180 kB pdf).
On the possible construction of a Mu2e calibration linac built around a spare Project-X or ILC cryomodule, July 25, 2008 (943 kB pdf).
The U.S. HEP community is currently discussing a reorganization of the university-based ILC R&D effort. See U.S. university engagement with the ILC: a report to the Americas Regional Team (356 kB pdf).
A neat idea, but probably not feasible due to nonlinear effects: a "Fourier Series Pulse Compression Kicker" for the ILC's damping rings. Here's a long technical memo about it: Performance Modeling of a Fourier Series Pulse Compression Kicker for the International Linear Collider Damping Rings (845 kB MSW).
I was a Proposal Coordinator for the Linear Collider Research and Development Working Group.
Fermilab International Linear Collider damping ring work: Studies Pertaining to a Small Damping Ring for the International Linear Collider.
My LCRD proposals... LCRD 2.15: Investigation of Acoustic Localization of rf Cavity Breakdown (1.7 MB pdf, complete with two movies [4.9MB and 12.5 MB]!) and LCRD 2.22: Investigation of Novel Schemes for Injection/Extraction Kickers (2.2 MB pdf).
2007 progress report from LCRD 2.22
Neutrino Mixing I: An Introduction to the Phenomenology
Brown bag lunch talk to UIUC HEP group; 2/20/01. 1.05 MB pdf.
Neutrino Mixing II: Oscillation Results and Experiments
Another brown bag lunch talk to UIUC HEP group; 2/27/01. 3.47 MB pdf.
CLEO III analog trigger work
I spent the 1998-99 school year on sabbatical at the Centre de Physique des Particules de Marseille, working on ATLAS silicon pixel detector issues. (We lived in Cassis, just east of Marseille.)